1. Field of the Invention
The present invention relates to precursor compositions in the form of a tape that are useful for the deposition of electronic features such as conductors, resistors and dielectrics by transferring the tape to a substrate. The tape materials can also have a low conversion temperature to enable low-temperature treatment of the tape to form electronic features on a variety of substrates. The tape compositions can also be disposed on a carrier to form a mechanically robust ribbon structure.
2. Description of Related Art
The electronics, display and energy industries rely on the formation of coatings and patterns of various materials such as conductors, dielectrics and resistors, to form circuits on organic and inorganic substrates. The primary methods for generating these patterns are screen printing for features larger than about 100 μm and thin film and etching methods for features smaller than about 100 μm. Other subtractive methods to attain fine feature sizes include photo-patternable pastes and laser trimming.
Another method that is known in the art is the transfer of material from one surface (a carrier) to another surface (a substrate) by some force, such as mechanical force.
For example, U.S. Pat. Nos. 6,177,151 by Chrisey et al. and 6,025,026 by Smith et al. disclose the use of laser transfer from a tape to fabricate a variety of electronic end products. The tape includes a composition that increases in volatility during transfer.
U.S. Pat. No. 5,645,932 by Uchibori discloses the use of a tape with an adhesive to attach conducting layers with stamping for patterning. A method to overcome the need for etching to provide layers is also disclosed.
U.S. Pat. No. 5,494,550 by Benge discloses a web driven approach for handling of tape. U.S. Pat. No. 5,211,984 by Wilson discloses decals and decal transfer methods for fuel cell component assembly. The decals are formed on a surface with a release layer and then laminated to another surface and separated from the backing. U.S. Pat. No. 4,826,554 by McIntyre et al. discloses methods for laminating to make fuel cell layers. U.S. Pat. No. 4,383,010 by Spaepen discloses rolling methods to make coatings for fuel cells and the like.
U.S. Pat. No. 6,207,268 by Kosaka et al. discloses a transfer sheet including a thermoplastic resin, a protective cover and a release layer. A resist is used to obtain patterns. The use of laser transfer and thermal heads is also disclosed.
U.S. Pat. No. 6,214,520 by Wolk et al. discloses thermal transfer and laser transfer for electroluminescent (EL) lamp manufacture. Light is used to heat a conversion layer to accomplish transfer. Conductor compositions disclosed include ATO, ITO, carbon and graphite.
U.S. Pat. No. 5,932,280 by Roth discloses thermally active coatings on ribbon. Transfer to a printed circuit board is accomplished by thermal processing. The use of precursors in the coating is not disclosed.
U.S. Pat. No. 5,826,329 by Roth discloses polymer thick film conductors formed from tape. U.S. Pat. No. 5,909,083 by Asano et al. discloses patterning tapes by etching through masks, particularly for glasses in plasma display applications. U.S. Pat. No. 5,992,320 by Kosaka et al. discloses transfer sheets and the details of their construction. U.S. Pat. No. 5,712,673 by Hayashi et al. discloses color transfer sheets. U.S. Pat. No. 4,105,483 by Lin discloses the transfer of material from printed paper. A solvent is applied, pressure is applied, and material is dissolved and removed to achieve transfer.
U.S. Pat. No. 5,665,472 by Tanaka et al. discloses the use of Bi—B—Si—O glass tapes and hot melt tape transfer to form patterns for plasma displays.
U.S. Pat. No. 5,998,085 by Isberg et al. discloses organic electroluminescent lamp fabrication methods. The deposition of phosphors by laser transfer is disclosed. Optional interlayers, thermal transfer layers and adhesive coatings are also disclosed.
U.S. Pat. No. 6,074,725 by Kennedy discloses applications of tape fabrication in microfluidics. Laminates are formed comprising structures between channels. The structures can be printed by laser, screen printing, ink-jet printing, precursor chemistry, and other approaches.
U.S. Pat. No. 5,953,037 by Hayashi et al. discloses tapes for color applications.
There is a need for compositions that provide electronic materials at low processing temperatures to allow deposition of the materials onto organic substrates with a fine minimum feature size, such as less than 200 μm, while still providing electronic features with adequate properties.
Precursor compositions for electronic materials such as conductors have been described by R. W. Vest (Metallo-Organic Materials for Improved Thick Film Reliability, Nov. 1, 1980, Final Report, Contract #N00163-79-C-0352, National Avionic Center). The compositions disclosed by Vest included a precursor and a solvent for the precursor. These compositions were not designed for processing at low temperatures, and as a result the processing temperatures were relatively high, such as greater than 250° C.
U.S. Pat. Nos. 5,882,722 and 6,036,889 by Kydd disclose conductor precursor compositions that contain particles, a precursor and a vehicle and are capable of forming pure conductors at low temperatures on organic substrates. However, the formulations are designed for screen printing of thick film electronic components. Materials to form transferable ribbon materials are not disclosed.
Polymer thick film materials containing particles in a polymerizable organic vehicle have also been disclosed in the prior art. These compositions are processable at low temperatures, such as less than 200° C., allowing deposition onto organic substrates. The compositions contain particles, usually flakes, at high loading and have a high viscosity. Ribbon and tape applications designed for transfer onto a substrate are not disclosed.
Attempts have been made to produce metal-containing compositions at low temperatures by using a composition containing a polymer and a precursor to a metal. See, for example, U.S. Pat. No. 6,019,926 by Southward et al. However, the deposits were chosen for optical properties and were either not conductive or were poorly conductive.
U.S. Pat. Nos. 5,846,615 and 5,894,038, both by Sharma' et al., disclose precursors to Au and Pd that have low reaction temperatures thereby conceptually enabling processing at low temperatures to form metals. It is disclosed that an ink jet can be used to apply the precursors.
U.S. Pat. No. 5,332,646 by Wright et al. discloses a method of making colloidal palladium and/or platinum metal dispersions by reducing a palladium and/or platinum metal of a metallo-organic palladium and/or platinum metal salt which lacks halide functionality. However, formulations for depositing electronic features are not disclosed.
U.S. Pat. No. 5,176,744 by Muller discloses the use of Cu-formate solutions for the direct laser writing of copper metal. The solutions prevent' crystallization of copper formate during drying.
U.S. Pat. No. 5,997,044 by Behm et al. discloses a document, such as a lottery ticket, having simple circuitry deposited thereon. The circuitry can be formed from inks containing conductive carbon and other additives as well as metallic particles. It is disclosed that the inks can be deposited by methods such as gravure printing.
U.S. Pat. No. 6,238,734 by Senzaki et al. is directed to compositions for the chemical vapor deposition of mixed metal or metal compound layers. The method uses a solventless common ligand mixture of metals in a liquid state for deposition by direct liquid injection.
The ideal tape composition and its associated deposition technique for the fabrication of electronic features such as a conductor would combine a number of attributes. The conductor would have high conductivity, preferably close to that of a dense, pure metal. The processing temperature would be low enough to allow formation of conductors on organic substrates. The deposition technique would allow deposition onto surfaces that are non-planar (e.g., not flat). The conductor would have high resistance to electromigration, solder leaching and oxidation. The conductor metal would be capable of forming an alloy with useful properties.
In the case of conductors derived from ribbon compositions containing combinations of precursors and particulates, a variety of criteria would be met. In one embodiment, the ribbon would be stable under ambient conditions, preventing compositional changes such as drying, enabling storage for extended times prior to transfer and processing. In another embodiment, the ribbon could be rolled and stored on a tape roll. The deposited material would not spread once deposited, to maintain the feature dimensions. The transferred material would have a high yield of conductor. In some cases where conductivity is the most desired characteristic, the final conductor would not contain polymers or other non-conductive materials. The deposit would adhere strongly to the surface and would be compatible with the substrate and other materials in contact with the conductor. The deposit would be flexible and mechanically strong. In cases where ease of processing is most critical, UV curable compositions would be desirable.
Further, there is a need for electronic circuit elements and complete electronic circuits fabricated on inexpensive, thin and flexible substrates such as paper using high volume printing techniques such as reel-to-reel printing. Recent developments in organic thin film transistor (TFT) technology have accelerated this need. These organic transistors will become key components of organic circuitry and low cost, disposable devices. This development highlights the emerging need for complimentary circuit elements that can be deposited directly onto low cost substrates. Such elements include conductive interconnects, electrodes, conductive contacts and via fills, resistors, capacitors, inductors, transformers, photoconductors, transparent electrodes, antennas, memory elements, electro-optical devices, optical modulators, optical wave guides, high frequency filters and modulators, rectifiers and a wide variety of sensors.